FMCW fill level measurement devices (FMCW: frequency-modulated continuous wave), and in particular FMCW fill level radar devices, should be relatively dynamic. In addition to the ability to process extremely small echo signals, the receiver of the fill level measurement device cannot be overdriven by very large echo signals.
In an FMCW fill level measurement device, echo signals having very low received power are often caused by objects that are far away. Echo signals having high received power often come from objects in the vicinity of the fill level measurement device. The distances between the fill levels to be measured to the antenna of the fill level measurement device can be from 0 m to well over 100 m. It is also possible for the antenna to protrude into the filling medium such that, in the case of an open horn antenna, the filling medium can also be located in the antenna horn.
So as to be able to process echo signals having such high dynamic ranges, circuits can be used which lead to time-dependent amplification control and thus cause dynamic compression. Methods of this type are known in radar technology as sensitivity time control (STC). In a receiver having STC functionality, the amplification is, for example, continuously increased during the receiving process. The amplification is therefore dependent on time and accordingly also on the distance between the fill level sensor and the surface of the filling medium. As a result, echo signals having short propagation times and correspondingly high received power are amplified to a lesser extent than signals having longer propagation times and lower power.
This propagation-dependent and thus distance-dependent amplification (or damping) of the echo signals can influence the curved shape of the echo curve, which in turn can influence the accuracy of the fill level sensor, in particular in the short range (i.e. for high fill levels).